Rotating flow combustor



July 24, 1956 FERRI ETAL 2,755,623

ROTATING FLOW COMBUSTOR Filed Feb. 19, 1953 INVENTORS Ania/22:0 firrz' BY 0 .Schwc rzf RGTATTNG FLOW COMBUSTQR Antonio Ferri, Rockville Centre, N. Y., and Ira R. Schwartz, Baltimore, Md.

Application February 19, 1953, Serial No. 337,895

4 Claims. (Cl. 60-3952) (Granted under Title 35, U. S. Code (1952), sec. 266) This invention relates to improvements in jet engines, particularly the combustors thereof.

In typical propulsion systems using turbine-driven axial flow compressors, one or more rows of stators are used at the outlet end of each compressor to. remove the rotation which is present rearward of the last rotor stage. if combustion in rotational flow in an annular combustion chamber were feasible and practical, the outlet stator rows could be eliminated, thus, losses associated therewith could be obviated and the mechanical design would be simplifled. The rotation of flow leaving the combustion chamber might also be advantageous in reducing the turning required of the turbine inlet nozzle. Accordingly, an object of the invention is to provide a jet engine of the axial flow type with a combustor that utilizes rotational flow instead of the customary axial flow thereby realizing the above advantages.

In addition, other advantages in the use of rotating flow in the combustor are found. Consider, for example, the flow about a flame holder located in a region of rotational flow where the velocity normal to the flame holder (axial velocity) is much smaller than the resultant of rotational and axial velocities, that is, the stream velocity. With such a burner, the velocity normal to the burner is fixed by volume of flow and flow area, whereas, the amount of turbulence present is determined by the resultant stream velocity. Combustion studies have shown that the rate of flame propogation is a function of the rate of energy transfer from the reacting to the unreacted flow and that the parameter most strongly affecting this rate is turbulence. The term reacting means involving a chemical change, such as combustion. Therefore, another object of the invention is to provide means for increasing lateral flame propagation rate by rotation of the flow in the combustor, for a given volume of flow.

Further objects of the invention are to shorten the combustion chamber length of jet propulsion systems by increasing combustion efliciency per unit length; eliminate unsteady burning conditions as manifested by vibrations and noises, that are frequently present in jet systems; and to prevent temperatures from becoming excessive when the air is decelerated from high to low Mach numbers.

Other objects and features will become apparent in following the description of the illustrated form of the invention.

The figure of the drawing is a perspective view of a combustor made in accordance with the teachings of the invention, portions being broken away in section to disclose internal detail.

In the drawing a typical embodiment of the invention is depicted as a combustor for a jet engine and it includes an annular casing together with an inner generally cylindrical core 12 held concentrically spaced from the inner surface of casing 16 by suitable braces that are not illustrated. The outer surface of core 12 coacting with the inner surface of casing 10 forms an annular flow passage 14, at the front end of which there is an inlet 16 is 2,755,623 Patented July 24, 1956 c CC 2 and at the rear end of which there is an exhaust outlet 18.

Conventional fuel supply or induction means, as manifold 20 with spray nozzles, are provided in passage 14 downstream of air inlet 16, and there is a flame holder 22 downstream of the fuel supply means 20. An initial ignition device, for example glow plug 24, is disposed in the passage 14 near the flame holder22, and it serves its usual function of initiating burning. Since burning takes place in passage 14 in the region of the flame holder, that part of passage 14 to outlet I8v is considered the combustion chamber, and it is in axial alignment with inlet 16 and outlet 18. i

In the usual case, a combustor as described this far would accept air at inlet 16 flowing axially of the passage, obtain fuel from fuel supply device 20, and the mixture would burn in the combustion chamber with the flame stabilized by flame holder 22. By increasing the axial velocity of air for a constant fuel flow rate, a condition of rough burning and intense noise precedes the point of flame blow off from flame holder 22. After the flame is detached from the flame holder, it is immediately extinguished, blowing out through outlet 18. It has been found that by rotating the air-fuel mixture through an angle as it progresses axially through passage 14, improved burning results are obtained. The specific angle may vary in accordance with combustor size and other factors, a tested case yielding excellent results when the turning angle was approximately seventy degrees from the axial direction. When rotating flow in passage 14 is present, no rough burning or excessive noise precedes the point of blow olf, as the air velocity through inlet 16 is increased. Moreover, upon attainment of sufficient air velocity, the flame is detached from flame holder 22 and establishes itself a short disance downstream of flame holder 22. A further increase in air velocity, well beyond the air velocity that caused the flame in the axial flow test to blow through outlet 18, moves the flame front slightly further downstream and an appreciable increase in entrance velocity is required to blow the flame completely from the combustion chamber. Hence, with rotational flow, the flame front may be stabilized at a selected station downstream of the flame holder.

The appearance of the flame pattern at the outlet 18 is quite diflerent with rotating flow from the appearance of the flame pattern with axial flow through passage 14. From the drawing, it is seen that the rotating flow is erally helical, and at outlet 18, the rotating flow flame is considerably shorter and possesses greater divergence with the attendant advantages thereof.

It is now established that rotating flow of the fuel-air mixture upon entry to the combustion chamber of a jet engine is superior to axial flow, and various means may be resorted to for obtaining such results. In the simplest case, the stators may be removed from the last compressor stage in a turbojet propulsion engine, thus allowing the air to retain its state of rotation as it leaves the last stage of rotors, and, after fuel injection into the rotating stream, the combustible mixture of air and fuel enters the combustion chamber while still rotating. Then the mixture would be burned in its rotating state in the combustors that are normally located immediately behind the last stage of compressor rotors. The drawing shows the use of an annular series of guiding vanes 26 connected to core member 12 and/or casing 10 and preferably located between the flame holder 22 and fuel supply device 29. Accordingly, axially moving air-fuel mixture passing through passage 14 has a rotary motion component imparted to it, diverting the mixture front as it approaches the flame holder 22. Upon burning, the helical pattern that started in the vanes 26 continues through as the flame in the combustion chamber and finally, through outlet 18.

It is understood that variations that fall within the scope of the claims may be made without departing from the protection thereof.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. In a jet engine combustor a casing, means in said casing coasting with the casing to define an annular flow passage having an air inlet at one end and an outlet at the opposite end, a fuel supplying device in said flow passage downstream of said air inlet, a flame holder downstream of said fuel supplying device, and means located in said passage between said device and said flame holder for stabilizing the fuel burning in said passage by imparting rotary motion concentric with said passage to the fuel-air mixture before it reaches said flame holder.

2. In a jet engine combustor a casing, means in said casing coacting with the casing to define an annular flow passage having an air inlet at one end and an outlet at the opposite end, a fuel supplying device in said flow passage downstream of said air inlet, a flame holder downstream of said fuel supplying device, and means located in said passage between said device and said flame holder for stabilizing the fuel burning in said passage by imparting rotary motion concentric with said passage to the fuel-air mixture before it reaches said flame holder, and said stabilizing means including a plurality of vanes.

3. For use in a jet engine, a combustor comprising a casing having an inlet and an outlet in axial alignment and having an annular flow passage and combustion chamber between said inlet and outlet, a flame holder disposed in said chamber, fuel induction means disposed in said casing upstream of said flame holder, and means for rotating the flow that passes into said inlet prior to reaching said flame holder through an angle of approximately seventy degrees from the axial direction so that the flow front contacts said flame holder at an angle with respect to the longitudinal axis of said passage, as a result of which the flame front is stabilized in addition to the stability attributable to the flame holder.

4. In a jet engine, an annular casing having an air inlet at one end, a combustion chamber and an outlet at the opposite end, said inlet, chamber and outlet being axially aligned, fuel induction means disposed in said casing downstream of said air inlet and upstream of said combustion chamber, a flame holder in said combustion chamber, and a plurality of vanes in advance of said flame holder to impart rotary motion concentric with the chamber to the air-fuel mixture that moves axially downstream of said fuel induction means.

References Cited in the file of this patent UNITED STATES PATENTS 2,603,945 Brown July 22, 1952 2,603,949 Brown July 22, 1952 2,654,996 Boninsegni Oct. 13, 1953 

